黄土高原生物结皮水土保持效应对干扰的响应及协同机理

Biological soil crusts are widely developed in the hilly Loess Plateau, which effectively prevent soil erosion from sloping land. However, the crusts also significantly reduce soil water infiltration, thus resulted a new pattern of soil erosion as "keep soil but loss water" with a worsen soil moisture conditions in the sloping land. To meet the demand of regional soil and water conservation and to overcome the reality issue of the contradictory function of biological crusts, the program was proposed based on the disturbance theory. Through located field plots monitoring under natural rainfall condition, the response of the micro-ecosystem structure of biological soil crusts (including biological community structure, morphology of biological soil crust and soil physicochemical composition, etc.), and soil and water conservation functions (i.e., rainfall permeability, erodibility and runoff, sediment) was investigated. The coupling and synergy mechanism between the micro ecosystem structure and soil-water conservation function of the biological crusts will be revealed based on the structural equation modeling. After understanding the possibility of synergizing the function contradictory through moderately disturbance, a quantitative relationship between disturbance and soil and water conservation function parameters will be established. In the view of “pursuing benefit and reducing defect", a program for synergizing the function contradictory through moderately disturbance will be proposed with the appropriate season and the corresponding degree of disturbance. The research results could provide a scientific basis for regional soil and water conservation as well as sustainable management of revegetated grassland. Meanwhile, the research could clear the coupling mechanism of ecosystem structure - function, and explore the possibility of synergizing the function contradictory through moderately disturbance.

黄土高原退耕地生物土壤结皮广泛发育，在有效防止坡面土壤流失的同时显著降低了土壤水分入渗，使退耕地形成“保土不保水”的水土流失格局，恶化了土壤水分状况。针对黄土高原水土流失防治需求与生物结皮“保土不保水”功能矛盾的现实问题，基于干扰理论，通过野外小区定位监测，利用自然降雨，研究干扰对生物结皮微生态系统结构（生物群落结构、结皮形态结构、土壤物质组成）及水土保持功能（渗透性、可蚀性及径流量、泥沙量）的影响，借助结构方程模型解析干扰条件下生物结皮微生态系统结构与水土保持功能间的耦合互馈机理，明确适度干扰协同生物结皮“保土不保水”矛盾的可能性，建立不同季节干扰度与水土保持功能指标间的量化关系，确定适宜的干扰季节及干扰度，提出生物结皮水土保持功能的协同方案，趋利除弊，为区域水土流失防治及退耕地的科学管理提供依据。对明确生态系统结构-功能耦合机理及适度干扰协同生态系统功能矛盾的可能性有科学价值。

黄土高原退耕地生物土壤结皮广泛发育，在有效防止坡面土壤流失的同时显著降低了土壤水分入渗，使退耕地形成“保土不保水”的水土流失格局，恶化了退耕地土壤水分状况。针对黄土高原水土流失防治需求与生物结皮“保土不保水”功能矛盾的现实问题，基于干扰理论，项目通过模拟降雨试验与自然降雨监测相结合的手段，研究了干扰对生物结皮生物群落结构、结皮形态结构、土壤物质组成及水土保持功能，包括渗透性、可蚀性、径流量和泥沙量的影响，在此基础上，借助灰色关联分析、结构方程模型等方法解析了干扰条件下生物结皮微生态系统结构与水土保持功能间的耦合互馈机理。结果表明干扰显著降低了演替后期的藻结皮、藓结皮和地衣结皮的盖度，影响程度与干扰度有关。干扰显著降低生物结皮层和其下0-2cm土层土壤有机碳含量，增加了生物结皮表面粗糙度和破碎度。干扰改善了生物结皮土壤渗透性，生物结皮土壤水分渗透性在10%-40%干扰度时随干扰度呈增加趋势，50%干扰条件下土壤水分渗透性较不干扰增加50%以上，径流系数较不干扰降低30.1%。50%以下的干扰未显著影响生物结皮土壤抗侵蚀性，坡面土壤产沙量与不干扰无差异。干扰增加了根层土壤储水量，40% 和50%干扰条件下年均土壤储水量较不干扰增加16.3%和34.0%，进而促进了退耕地植被生长发育。干扰主要通过影响生物结皮表面糙度和生物结皮破碎度进而改善其土壤水分渗透性。研究区50%干扰可较好的协同生物结皮“保土不保水”的功能矛盾，此干扰度下，坡面径流较不干扰减少53.2%，泥沙无显著变化。.研究明确了干扰协同生物结皮“保土不保水”功能矛盾的可能性，解析了干扰对生物结皮群落结构及水土保持功能影响的作用机制，提出了协同研究区水土保持功能矛盾的生物结皮干扰强度可能阈值，为黄土丘陵区退耕封禁地的科学管理和适度利用奠定了科学基础。